Method of forming a glossy surface



2,847,286 Martian or FORMING A GLOSSY SURFACE Heinrich Neunzig, Gindorf, Friedrich Baumann, Bad

Godesberg, and Werner Helling, Grevenbroich, Germany, assignors to Vereinigte Aluminum-Werke Aktiengesellschaft, Bonn, Germany No Drawing. Application December 20, 1955 Serial No. 554,130

@Claims priority, application Germany December 23, 1954 15 (Zlaims. (Cl. 41-42) The present invention relates to a method of forming a glossy surface and more particularly it relates to a. method of forming a glossy surface on an aluminum body.

Various treating solutions are known by means of which it has been attempted to form a glossy surface on an aluminum body, or to substantially increase the gloss of such a surface. While it is comparatively easy to obtain a certain amount of gloss on pure aluminum surfaces such as having a purity of 99.99% of aluminum, great difficulties are encountered in forming a glossy surface on aluminum products the purity of which is only 99.9%, 99.85% or less. Similarly, great difficulties are encountered when it is attempted to obtain a highly shining, glossy surface on objects made of aluminum alloys, such as aluminum alloys which contain limited quantities of magnesium, or of magnesium and silicon, especially when the aluminum component of these alloys has a purity of only 99.85% or 99.9%. Even for treating aluminum of the highest purity so as to obtain a highly glossy surface, it was necessary to employ relatively high concentrations of treating chemicals and consequently to use considerable quantities of the same. 7

It is therefore an object of the present invention to overcome the aforedescribed difficulties in forming glossy surfaces on objects made of aluminum and aluminum alloys. i

It is another object of the present invention to provide a method and treating solution for producing glossy surfaces on objects made of aluminum and aluminum alloys which are effective and economical.

It is a further object of the present invention .to provide means for forming a glossy surface on an aluminum body which will be effective regardless whether the aluminum is of high grade, commercial or low purity,

and which will also be effective when used in connection with aluminum alloys. I

it is still another object of the present invention to provide means for forming glossy surfaces on aluminum or aluminum alloy bodies in such a. way that the degree of gloss can be effectively controlled.

Other objects and advantages of the present invention will become apparent from a further reading of the description and the appended claims.

With the above objects in view, the present invention mainly comprises in a method of forming a glossy surface on an aluminum body, the step of treating the surface for a period of between 8 and 30 seconds at a. temperature of between 40 and 90 centigrade with an aqueous solution containing as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025% and 0.2% by weight of lead ions, whereby a glossy surface is formed on the body.

The present invention also comprises as a new composition of matter a treating solution forming a glossy surface on an aluminum body, the treating solution esentially consisting of water having dissolved therein as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight of hydrofates Patent fluoric acid, and between 0.025%, and 0.2% by weight of lead ions. I

According to the present invention it is now possible to achieve a high gloss on bodies made of aluminum and aluminum alloys by using treating solutions of relatively low concentration and of a simple composition, and also to obtain a high gloss on aluminum surfaces which have an aluminum content of considerably less than 99.99%. Similarly, it is possible according to the present invention to obtain a high gloss on surfaces of bodies of aluminum alloys which were produced with an aluminum of low purity.

According to the present invention an acidic treating solution is used which contains between 1.2% and 9.5% of nitric acid, between 2% and 14% of hydrofluoric acid, and between 0.025% and 0.2% of lead ions. All percentage figures given above and used further below in the present application refer to percent by weight of the entire treating solution. The lead ions which are present in the treating solution of the present invention are Supplied by dissolving in the treating solution an acid-soluble lead salt, such as lead nitrate, lead fluoride, lead chloride,

or lead acetate. Preferably the concentration of the nitric acid in the treating solution is kept between 2.9 and 5.8% by weight and the concentration of the hydrofluoric acid between 4.4 and 8.8% by weight. The best results according to the present invention are obtained on an aluminum or aluminum alloy surface by using a treating solution which contains approximately 4.35% of nitric acid, 7% of hydrofluoric acid and 0.125% of lead These relatively weak, and consequently very economical, solutions arepreferably used at a temperature of between 40 and 90 C. and most preferably at a temperature between and 60 C. Treating time according to the present invention has to be between about 8 and 30 seconds. By treating an aluminum or aluminum alloy surface with a solution containing approximately 4.35% of nitric acid, 7% of hydrofluoric acid and 0.125% of lead ions for a period of between 8 and 30 seconds, depending on the exactcomposition of the surface material, and a temperature of preferably between 50 and 7 60, mirrorlike, highly glossy surfaces are obtained with aluminum of high purity as well as with aluminum of low purity, and with aluminum alloys.

According to the method of the present invention it is possible to obtain a predetermined degree of gloss. By keeping the bath concentration between about 1.2 and 2.9% of nitric acid or between 5.8 and 9.5% of nitric acid and between 2.0 and 4.4%, or between 8.8 and 14% of hydrofluoric acid, while keeping the lead ion concentration between 0.025% and 0.2%, a lesser, somewhat duller degree of gloss is obtained. If, however, a concentration of about 4.35% by weight of nitric acid and about 7.0% of hydrofluoric acid is maintained in the treating solution which also contains between 0.025% and 0.2% by weight of lead ions, then a highly glossy, mirror-like surface is achieved.

The glossy eifect is-increased according to the present invention and the loss of Weight of the aluminum or aluminum alloy body during treatment is decreased by adding to the above described treating solution according to the present invention a solution-retarding substance such as gum arabic or a solution-retarding colloidal polysaccharide. Excellent results have been obtained by using either gum arabic or deXtrin as solution-retarding colloidal substance. The solution-retarding colloidal substance is preferably added to the treating solution in a quantity of between 0.4 and 2% by weight. Excellent results were obtained by adding 1% by weight of either gum arabic or dextrin to the treating solution.

The glossy surfaces formed according to the present invention may subsequently also be provided with an oxide layer by anodizing or other chemical methods. It is also possible to further treat the glossy surfaces formed according to the present invention so as to color the same.

The following examples are given as illustrative only, the present invention however not being limited to the specific details shown in the examples:

Aluminum objects were treated according to the present invention by being immersed in the treating solution for the time indicated in the individual examples. The objects were then removed from the treating solution, any treating solution adhering to the objects was immediately washed off with water, and the objects were then allowed to dry.

The result obtained in eleven different examples are summarized in Table I in which for each example the composition of the surface portion of the aluminum body, the concentration in percent by weight of nitric acid, hydrofluoric acid and lead ions in the treating solution, the treatment temperature, and the treatment time are shown. It is also indicated in the table whether any solution-retarding substances were added to the treating solution, and if so, what substance and in what amount. Furthermore, the lead salt is identified which in each case has been used in order to supply the indicated quantity of lead ions in the treating solution. The degree of gloss obtained according to the individual examples is Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairlyconstitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a method of forming a glossy surface on an aluminum body, the step of treating said surface for a period of between 8 and seconds at a temperature of between and 90 centigrade with an aqueous solu tion free of ammonium ions and containing as active ingredients between 1.2% and 9.5 by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025 and 0.2% by weight of lead ions, whereby a glossy surface is formed on said body.

2. In a method of forming a glossy surface on an aluminum body, the step of immersing said body for a period of between 8 and 30 seconds in an aqueous solution free of ammonium ions and having a temperature of between 40 and 90 centigrade and containing as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025% and 0.2% by weight of lead ions, whereby'a glossy surface is formed on said recorded as specular reflectivity, and as total reflectivity. 30 body.

Table I In Solution: in per- Treatment Reflectivity Composition cent by weight Example of Aluminum Number Body HNO; HF Pb Temp. Time Specular, Total,

ions 1 m C. in Sec. Percent Percent 4. 35 7.0 0. 125 15 90.0 91. 5 4. 35 7. 0 0. 125 50 15 78. 0 90. 1 4. 35 7.0 0. 125 50 15 74. 0 89.0 1. 2 2. 5 0. 025 80 30 85. 0 92.0 1.2 2. 5 0. 125 80 30 65. 0 91. 0 Al99.99% 2. 9 5. 0 0. 025 60 20 86. 0 92. 0 Al9).99% 2. 9 5.0 0.125 60 20 87. 0 92. 0 2. 9 5.0 0. 200 60 20 84. 0 92. 0 9. 5 9.0 0. 025 40 10 80.0 91. 0 9. 5 9. O 0. 125 40 10 75. 0 91. 0 9. 5 9.0 0. 200 40 10 70.0 91. 0

1 The Pb ions in Examples 1, 4, 6 and 8 were formed by dissolving lead nitrate, in Ex- 11 by dissolving lead 5 and 7 by dissolving lead acetate in the aqueous solution of eatrnent solution employed in Examples 1-3 also contained 1.0% by weight of 3 The treatment solution employed in Example 9 also contained 1.5% by weight of doxtrin.

Examples 1, 2 and 3 were then repeated omitting the addition of gum arabic, while in every other respect completely conforming to Examples 1, 2 and 3. The specular reflectivity of the thereby glossy surfaces was then measured and compared with the specular reflectivity obtained according to Examples 1, 2 and 3 as indicated in Table II.

Table 11 Example Number Specular Reflectivity 0 "th 1: in arabic .2 i .".f .f 7 2 'th, t um arabic .fi f.. 74. 0 3 without gum arabic 4o 5 Table II clearly shows the further increase in gloss which is obtained by treating an aluminum surface with a treating solution according to the present invention to which a solution-retarding colloidal substance has been added.

3. In a method of forming a glossy surface on a body of an aluminum alloy consisting mainly of aluminum, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight 'of hydrofluoric acid, and between 0.025% and 0.2% by weight of lead ions, whereby a glossy surface is formed on said body.

4. In a method of forming a glossy surface on an aluminum body consisting of commercial aluminum and its homogeneous aluminum-magnesium alloys and its homogeneous aluminum-magnesium-silicon alloys with up to 0.06% Fe and with up to 0.05% Cu, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025% and 0.2% by weight of lead ions formed by dissolution of an acid-soluble lead salt, whereby a glossy surface is formed on said body.

5. In a method of forming a glossy surface on a body of a substance belonging to the group consisting of aluminum with up to 0.06% Fe and 0.05% Cu, alloys of aluminum with up to 0.8% silicon and up to 2.5% magnesium, and alloys of aluminum with up to 2.7% magnesium, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025% and 0.2% by weight of lead ions, whereby a glossy surface is formed on said body.

6. In a method of forming a glossy surface on a body of a substance belonging to the group consisting of aluminum with up to 0.06% Fe and 0.05% Cu, alloys of aluminum with up to 0.8% silicon and up to 2.5% magnesium, and alloys of aluminum with up to 2.7% magnesium, the step of treating said surface for a-period of between 8 and 30 seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 2.9% aud 5.8% by weight of nitric acid, between 4.4% and 8.8% by weight of hydrofluoric acid, and approximately 0.125% by weight of lead ions, whereby a glossy surface is formed on said body.

7. In a method of forming a glossy surface on a body of a substance belonging to the group consisting of aluminum with up to 0.06% Fe and 0.05% Cu, alloys of aluminum with up to 0.8% silicon and up to 2.5 magnesium, and alloys of aluminum with up to 2.7 magnesium, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients be tween approximately 4.35% by weight of nitric acid, approximately 7% by weight of hydrofluoric acid, and approximately 0.125% by weight of lead ions, whereby a glossy surface is formed on said body.

8. In a method of forming a glossy surface on an aluminum body, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025 and 0.2% by weight of lead ions, and also containing a colloidal substance adapted to retard dissolution of said body in said aqueous solution, whereby a glossy surface is formed on said body.

9. In a method of forming a glossy surface on an aluminum body, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 1.2% and 9.5 by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025% and 0.2% by weight of lead ions, and also containing between 0.4% and 2% by weight of a colloidal substance belonging to the group consisting of gum arabic and polysaccharides adapted to retard dissolution of said body in said aqueous solution, whereby a glossy surface is formed on said body.

10. In a method of forming a glossy surface on an aluminum body, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 1.2% and 9.5 by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025% and 0.2% by weight of lead ions, and also containing between 0.4% and 2% by weight of 6 dextrin, whereby a glossy surface is formed on said body.

11. In a method of forming a glossy surface on an aluminum body, the step of treating said surface for a period of between 8 and seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025 and 0.2% by weight of lead ions, and also containing between 0.4% and 2% by weight of gum arabic, whereby a glossy surface is formed on said body.

12. In a method of forming a glossy surface on a body of a substance belonging to the group consisting of aluminum with up to 0.06% Fe and 0.05% Cu, alloys of aluminum with up to 0.8% silicon and up to 2.5% magnesium,. and alloys of aluminum with up to 2.7% magnesium, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and 90 centigrade with an aqueous solution free of ammonium ions and containing as active ingredients between 1.2% and 9.5 by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and between 0.025 and 0.2% by weight of lead ions formed by dissolution of a lead salt belonging to the group consisting of lead nitrate, lead fluoride, lead chloride and lead acetate, whereby aglossy surface is formed on said body.

13. In a method of forming a glossy surface on a body of a substance belonging to the group consisting of aluminum with-up to 0.06% Fe and 0.05% Cu, alloys of aluminum with up to 0.8% silicon and up to 2.5 magnesium, and alloys of aluminum with up to 2.7 magnesium, the step of treating said surface for a period of between 8 and 30 seconds at a temperature of between 40 and centigrade with an aqueous solution free of ammonium ions and containing as active ingredients approximately 4.35% by weight of nitric acid, approximately 7% by weight of hydrofluoric acid, and approximately 0.125 by weight of lead ions formed by a dissolution of an acid-soluble lead salt, and also containing between 0.4% and 2% by weight of a colloidal substance belonging to the group consisting of gum arabic and polysaccharides adapted to retard dissolution of said body in said aqueous solution, whereby a glossy surface is formed on said body.

14. As a new composition of matter a treating solution adapted to form a glossy surface on an aluminum body, said treating solution essentially consisting of water having dissolved therein as active ingredients between 1.2% and 9.5% by weight of nitric acid, between 2% and 14% by weight of hydrofluoric acid, and'between 0.025% and 0.2% by weight of lead ions, the thusformed solution being free of ammonium ions.

15. As a new composition of matter a treating'solution adapted to form a glossy surface on an aluminum body, said treating solution essentially consisting of water having dissolved therein as active ingredients approximately 4.35% by weight of nitric acid, approximately 7% by weight of hydrofluoric acid, and approximately 0.125%

by weight of lead ions, and also containing between 0.4%

and 2% by weight of a colloidal substance belonging to the group consisting of gum arabic and polysaccharides adapted to retard dissolution of said body in said aqueous solution, the thus-formed solution being free of ammonium ions.

References Cited in the file of this patent UNITED STATES PATENTS 2,614,913 Reindl et a1. Oct. 20, 1950 2,746,849 Helling et al. May 22, 1956 FOREIGN PATENTS 1,082,346 France Dec. 28, 1954 

1. IN A METHOD OF FORMING A GLOSSY SURFACE ON AN ALUMINUM BODY, THE STEP OF TREATING SAID SURFACE FOR A PERIOD OF BETWEEN 8 AND 30 SECONDS AT A TEMPERATURE OF BETWEEN 40* AND 90* CENTIGRADE WITH AN AQUEOUS SOLUTION FREE OF AMMONIUM IONS AND CONTAINING AS ACTIVE INGREDIENTS BETWEEN 1.2% AND 9.5% BY WEIGHT OF NITRIC ACID, BETWEEN 2% AND 14% BY WEIGHT OF HYDROFLUORIC ACID, AND BETWEEN 0.025% AND 0.2% BY WEIGHT OF LEAD IONS, WHEREBY A GLOSSY SURFACE IS FORMED ON SAID BODY. 